Conventionally, quickly cookable foods like chow mein, spaghetti, polished rice and sekihan (steamed rice with red beans) or the like have been distributed as a sort of quickly cookable foods to be cooked by pouring thereinto hot water, leaving it for a predetermined time and removing therefrom the hot water.
As the containers for quickly cookable foods, as illustrated in FIG. 12(A), the present Applicant had proposed a sheet-form lid member 100 having the layered structure in which the surface sheet 111 is laminated onto the composite sheet 101. With reference to FIG. 12(B), this lid member 100 is a circular lid member when it is viewed horizontally, then the surface thereof is sectioned into the easily-peelable area A and the non-peelable area B having the aforementioned layered structure. Further, the easily-peelable area A has the easily-peelable layer 105 formed by applying lubricant (smooth releaser; e.g., release varnish) between the surface sheet 111 and the composite sheet 101.
Circular slits 107 of inner diameter R for apertures are entered vertical-sectionally into the easily-peelable area A in the composite sheet 101, and a bond area 106 (where the easily-peelable layer 105 is not formed) of the inner diameter r is formed in the back of the surface sheet 111 to be contacted with cut area made on the composite sheet 101 by the slit 107. Since the composite sheet 101 is adhered to the surface sheet 111 through contact area 106, when the surface sheet 111 is peeled from the composite sheet 101, the slit 107 is simultaneously broken, thereby, apertures are formed in the composite sheet 101. Then, as illustrated in FIG. 13, a container for the instantly cookable foods are made by adhering (e.g., heat-sealing) the lid member 100 onto the flange 121 of the container 120 for the instantly cookable foods, and hermetically packing the container.
Hermetically packed container 120 is opened, for example, by pulling up tab 113 integrally made of the composite sheet 101 at the outer circumference of the non-peelable area B, and peeling a part of the lid member from the flange 121. Then, after pouring the hot-water into the container 120, the tab 113 is again bent over toward the flange 121 to reseal the container 120. After then, it is left for several minutes to cook the instantly-cookable foods (not shown) in the container.
Then, apertures are formed in the composite sheet 101 by pulling up tab 112 integrally made of the surface sheet 111 at the outer circumference of the lid member 100, and peeling the easily-peelable area A in the surface sheet 111 from the composite sheet 101. Thereafter, unnecessary hot water in the container 120 is discharged from such apertures.
Slits 107 of inner diameter R are made to include whole of the contact area 106 of inner diameter r and a part of the easily-peelable layer 105. But, due to peeling of the easily-peelable layer 105, the surface sheet 111 is unpredictably peeled along the outline of the contact area 106 when it receives pressure or impact by the molded blades.
Since such diameters R and r are typically approximate values, precise registration is necessary to register the mutual positions of the areas cut by the slit 107 and the easily-peelable layer 105. Actually, in such cases, considerable skilled techniques are needed to apply lubricant minutely and to register the layers precisely, and production loss on the lid member would not be avoided.
Then, when the surface sheet 111 in the easily-peelable area A is going to be peeled from the composite sheet 101, the surface sheet 111 is not peeled straightly along the slit 109 formed previously, and the surface sheet is torn (picked), figure of the lid member 100 therefore became unfavorable.
Such matters happen when the peel strength between the surface sheet 111 in the easily-peelable area A and the composite sheet 101 is large, or when mutual position therebetween is not registered well.
As a conventional lubricant, it may include and use a thermo-plastic resin such as a urethane resin, polyamide resin or the like, nitrocellulose resin, or the lubricant (the release varnish) containing a combination of these resins as a main ingredient. But, according to these lubricants, in the production of the lid member 100, lubricant width has to be restricted to the narrower width of 20 through 40 g/15 mm in view of peelability (peel strength) of the surface sheet 111. As a result thereof, continuous production of the lid member would be difficult, in addition thereto, peelability of the surface sheet 111 is poor and the surface sheet 111 cannot be peeled smoothly at the peeling thereof.
Conventional lid member as illustrated in FIG. 12 may therefore not have enough peelability on the surface sheet 111 in the easily-peelable area A, in particular, inconvenient picking might not be avoided in the paper surface sheet 111.
The present invention is aimed to relax such duties for applying the lubricants aforenoted as well as necessary work to register the mutual position between the composite sheet 101 and the surface sheet 111, while qualities on the lid member is improved by preventing unpredictable peeling, with the easily-peelable layer 105, of the surface sheet 111 along the outline of the contact area 106.
The present invention is aimed to realize the lid member which can smoothly peel the surface sheet from the composite sheet and can easily expose/form the apertures without picking the paper surface sheet 111.